A flash channel changes (degrades) over time with program-erase cycles (PECs), retention, and read disturb effects. An effective detection and coding/decoding solution needs to adapt to the changes in the flash channel. Typically, detector/decoder designs are governed by an assumed channel model. Such channel models are described or defined by a set of parameters. A typical model for a flash cell uses pulse-amplitude modulation (PAM) signaling with an additive white Gaussian noise (AWGN) channel. An AWGN channel with 4-PAM signaling is parameterized with four means corresponding to signal amplitudes and four sigmas corresponding to the one-sided power spectral density of the AWGN. Adaptations to the changes in the flash channel are based on a channel tracking mechanism using statistics collected for an adaptive tracking algorithm to track variations in the channel and consequently, update the set of channel parameters. The updated set of channel parameters is used to adjust hard/soft read reference voltages, re-compute bit reliability messages, etc. The channel tracking mechanism may also be used to estimate inter-cell interference (ICI) and variation in ICI over time.
It would be desirable to have a framework for balancing robustness and latency during collection of statistics from soft reads of the flash channel.